1. Field of the Invention
The present invention relates to a method and a device for setting a bending process when a plate-shaped workpiece is bent by a bending machine such as a press brake or the like, and also to a method for preparing bending data.
2. Description of the Prior Art
Generally, in a bending machine such as a press brake or the like, when a workpiece W is subjected to a bending process, for example, when a product of a shape such as shown in FIG. 1 is obtained, first a 90.degree. bending process is carried out at a bending point 2, then the workpiece W is rotated from top to bottom and the same 90.degree. bending process is performed at a bending point 1.
However, with this type of bending process, when the bend at the bending point 2 has been completed and the workpiece W is set on a lower die D to make the bend at the bending point 1, as shown by a solid line in FIG. 2(a), the workpiece W interferes with the lower die D and a situation is created wherein it becomes impossible to set the workpiece W on the specified position on the lower die D.
Accordingly, as shown in FIG. 2(b), in order to perform bending process in which the 90.degree. bend is performed at bending point 1 after the same is done at bending point 2, it is necessary to use the so-called "preparatory bending process" to avoid interference with the lower die D. In the preparatory bending process, bending is preliminarily carried out to a shallow bending angle at the bending point 1, and after the bending process at the bending point 2, bending is again performed at the bending point 1, and a true 90.degree. angle is obtained at the bending point 1.
In the abovementioned "preparatory bending process" the workpiece W is not processed to the final angle at the bending point in one step. The first part of the process is an obtuse angle bend; the second part is a final bend to obtain the required object angle.
FIG. 3 shows the abovementioned preparatory-bending process. As shown in FIG. 3 (a), one end O of the workpiece W is impacted by a striking member C of the bending machine, and the preparatory bend is performed at a shallow bending angle at the bending point 1. Next, as shown in FIG. 3 (b), the workpiece W is rotated and the bending is completed to produce a true 90.degree. angle at bending point 2. Following this, as shown in FIG. 3 (c), additional bending is again performed at the bending point 1 to reach a 90.degree. angle, which is the final objective bending angle.
However, with a conventional bending machine, there is no known method of setting the process in which this type of preparatory bending can be performed automatically. In addition, there is no known device which will automatically check for interference between the lower die and the workpiece in an NC device for a bending machine, or which will, in the case where there is concern that such interference will be produced, automatically set the preparatory bending process and set the process to avoid interference between the die and the workpiece.
In recent years, in the field of bending processing, which still must resort to manual operation, a process has been developed by which bending data has been prepared semi-automatically: while the actual bending status is being simulated for set bending dies, bending data for determining the amount of movement of the back gauge of the bending machine and the dies for the set bending dies and bending sequence, can be drawn up semi-automatically.
Conventionally, in the method of drawing up this bending data, when there is interference between the workpiece and the mold, this condition is displayed on the simulation screen to advise the operator.
Therefore, conventionally, the operator changes the bending sequence or the dies based on the data indicating that interference exists. The question as to whether new dies should be fabricated is decided from the criterion of the amount of interference; after the interfering portion of the dies is suitably removed to avoid the interference, once again an interference check is made. In most case, it is possible to eliminate this interference by changing the bending sequence or changing the dies, but, to prevent adverse effects on the shape of the product and the precision of the bend, there are occasions when it is impossible to change the bending sequence or the dies.
However, in the method of drawing up bending data in the abovementioned conventional manner, in the case where there is interference between the workpiece and the dies, there is only a report indicating that interference exists; therefore, when an additional process is to be performed at the dies in order to eliminate the interfering portion of the dies to avoid subsequent interference between the workpiece and the dies, the operator must prepare the data for the additional processing to take off part of the dies, based on this information. The problem exists that a great deal of time and trouble is necessary to prepare this data for this additional process.
In addition, when there is interference between the mold and the workpiece, the process of drawing up the bending data is halted at this point so that after the additional processing on the die, the bending data must therefore be revised and prepared again.